ACTH inhibits cell proliferation with a concomitant stimulation of steroidogenesis in functional mouse adrenal tumor cells(Y-l). Y-l cells require serum for growth and steroidogenic response to ACTH. The substances responsible for these events will be elucidated and the role of cAMP and cGMP will be investigated. To study the relationship between cell function (steroidogenesis) and growth in these tumor cells, we have isolated ACTH- or cAMP-resistant mutants. The properties of these mutants will be characterized in detail. ACTH treatment inhibits the growth of transplanted Y-l cells. ACTH- or cAMP resistant mutant cells will be injected into mice and the effects of ACTH- or cAMP-treatment on their growth will be studied. In normal animals ACTH treatment stimulates cell proliferation in the adrenal cortex. To elucidate the mechanism of this stimulatory effect of ACTH, it is desirable to establish an adrenal cell line in tissue culture, the growth of which is stimulated by ACTH. In the first step of this approach, primary culture of the adrenal glands will be used. Also, we have been trying to produce ACTH-dependent adrenal tumors by injecting adrenal cells into spleens of adrenectomized animals.